DNA tests

One area that causes frequent misunderstanding is the phenomenon of germ line mosaicism.
Here's a typical question (actually a composite of several queries to "Ask the Experts"):
Five years ago, I gave birth to a child with Duchenne muscular dystrophy (DMD). At that time, they tested my blood cell DNA and said I didn't have the deletion in my dystrophin genes that causes DMD. My son, Danny,...